Coprocessing method for co-hydrothermal liquefaction of polyamide 6 and polycarbonate

Abstract

The invention discloses a coprocessing method for co-hydrothermal liquefaction of polyamide 6 and polycarbonate. The coprocessing method comprises the following steps: (1) pretreating PA6 and PC raw materials; (2) mixing the pretreated PA6 and PC in proportion; (3) carrying out hydrothermal liquefaction treatment on the obtained mixture; (4) separating and purifying a product subjected to hydrothermal liquefaction treatment; (5) using a separated liquid-phase product for monomer recovery; (6) carrying out subsequent treatment on separated solid-phase residues; wherein the mass ratio of PA6 to PC in the step (2) is 1: 1; in the step (3), the temperature of the hydrothermal liquefaction treatment is 240-300 DEG C, and the reaction time is 60 minutes. According to the invention, the special environment of hydrothermal reaction is utilized to realize the synergistic depolymerization of PA6 and PC. Under the condition of 270 DEG C / 60 min, the PA6 solid hydrolysis degree reaches 100%; the PC oil phase yield reaches 79.78%; and the CPL yield is kept at 33.98% (not obviously reduced). Compared with single treatment, the reaction temperature is reduced by 30-50 DEG C, and the energy consumption is obviously reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste treatment, and particularly relates to a synergistic treatment method for hydrothermal co-liquefaction of polyamide 6 and polycarbonate. BACKGROUND

[0002] The widespread application of plastics has led to the generation of a large amount of mixed plastic waste, which seriously damages the ecological system and endangers human health, making plastic waste management one of the most severe environmental challenges in the 21st century. Among them, polycarbonate (PC) has become the fastest-growing variety in the field of general engineering plastics due to its excellent mechanical properties, thermal stability and chemical stability; and polyamide 6 (PA6) is one of the highest-yield polyamides, with high chemical stability, elasticity, tensile strength and wear resistance. Therefore, efficient recovery of PC and PA6 has become a key issue in the sustainable research of polymers.

[0003] In recent years, hydrothermal technology has been widely used in plastic treatment. Hydrothermal liquefaction (HTL) is carried out under sub- / super-critical water conditions, and the water medium has a dual role of solvent and catalyst through the reduction of dielectric constant and the increase of ionic product, which can accelerate the hydrolysis of polymer chains and decompose them into monomers or low molecular weight compounds, thereby realizing efficient resource recovery. Unlike traditional polyolefins (such as PP, PE), PC and PA6, as condensation polymers, have chemical instability in ester bonds and amide bonds in their molecular chains, and thus are more suitable for hydrothermal chemical recycling.

[0004] Existing research shows that the highest carbon liquefaction efficiency of PC can reach 57.70wt% when hydrothermally treated at 300-500℃, and the main products are phenol (29.2%) and 4-isopropyl phenol (19.1%); the addition of Na2CO3 can accelerate the decomposition of PC, and the product yield can reach 67% when reacted at 300℃ for 24 hours. In addition, acidic catalysts (such as HCl, phosphotungstic heteropoly acid, zeolite, etc.) can significantly reduce the activation energy of PA6 hydrolysis, and when a 3wt% phosphotungstic heteropoly acid catalyst is used, the caprolactam yield can be increased to 78.0% when reacted at 300℃ for 85 minutes.

[0005] Most existing researches focus on the treatment of single plastic, ignoring the interaction mechanism between the degradation products of different plastic wastes. For example, previous studies have found that the HCl produced by the co-treatment of PVC and PA66 can significantly reduce the hydrolysis temperature of PA66, while the co-treatment of PET and PA6 leads to a 20% decrease in terephthalic acid recovery rate, indicating that different polymer combinations have significant synergistic / antagonistic effects. The existing technology has the following technical problems:

[0006] 1. Low efficiency of single plastic treatment: Traditional hydrothermal technology is aimed at single plastic, and the depolymerization efficiency is limited, and high temperature, long time or strong acid / strong base catalysts are required, which is high in energy consumption and easy to cause secondary pollution.

[0007] 2. Mixed plastic synergistic treatment research is missing: existing research focuses on single plastic, while actual waste is mostly mixed (such as PC / PA6), the synergistic / antagonistic effect between different plastic degradation products is unknown, making it difficult to optimize reaction conditions during co-treatment.

[0008] 3. Process relies on trial and error: key parameters such as temperature and time for mixed plastic co-treatment lack theoretical guidance and need to be optimized through repeated experiments, which restricts process development efficiency and makes it difficult to meet the demand for efficient recycling of actual mixed waste.

[0009] 4. Bottleneck for engineering applications: there is a serious lack of co-treatment technology for typical mixed engineering plastics such as PC / PA6, and existing methods cannot achieve efficient and synergistic depolymerization under mild conditions, limiting large-scale applications. SUMMARY

[0010] The present application provides an optimized co-hydrothermal liquefaction synergistic treatment method to address the low monomer recovery rate, harsh reaction conditions, and underutilization of synergistic effects during the hydrothermal liquefaction of mixed polyamide 6 (PA6) and polycarbonate (PC) plastics. The method aims to improve monomer recovery efficiency, reduce reaction energy consumption, and achieve synergistic effects between the two plastic degradation products by adjusting reaction conditions, providing a new strategy for efficient resource recovery of mixed plastics. The PC / PA6 synergistic co-hydrothermal liquefaction method provided by the present application achieves efficient depolymerization under mild conditions by optimizing reaction conditions (240-300°C, ≤60min) and utilizing the self-catalytic effect of degradation products, while reducing the dependence on catalysts. The present application reduces energy consumption while improving depolymerization efficiency (PA6 hydrolysis degree up to 100%, PC oil phase yield increased to 79.78%), providing an efficient and environmentally friendly solution for the resource recovery of mixed plastic waste.

[0011] The technical solution adopted by the present application to solve the above technical problems is:

[0012] A synergistic treatment method for co-hydrothermal liquefaction of polyamide 6 and polycarbonate, comprising the following steps:

[0013] (1) Pretreat PA6 and PC raw materials;

[0014] (2) Mix the pretreated PA6 and PC in proportion;

[0015] (3) Perform hydrothermal liquefaction treatment on the obtained mixture;

[0016] (4) Separate and purify the product after hydrothermal liquefaction treatment;

[0017] (5) Use the separated liquid phase product for monomer recovery;

[0018] (6) The separated solid residue is subjected to subsequent treatment.

[0019] In step (2), preferably, the mass ratio of PA6 to PC is 1:1, which ensures the full interaction of the two plastic degradation products and realizes synergistic depolymerization.

[0020] In step (3), the temperature of the hydrothermal liquefaction treatment is 240-300℃, and the reaction time is 60 minutes.

[0021] Further, the raw material pretreatment in step (1) includes the following steps:

[0022] (1) PA6: raw material with a density of 1.084 g / cm 3 , a melting point of 220℃, and a particle size of 30 mesh is selected;

[0023] (2) PC: raw material with a melt index of 5 g / 10 min (300℃ / 1.2 kg) is selected;

[0024] (3) The water content needs to be removed by vacuum drying at 60℃ for 12 hours before use.

[0025] Further, the specific conditions of the hydrothermal liquefaction treatment in step (3) are as follows:

[0026] Reaction pressure: autogenous pressure (about 10 MPa);

[0027] Stirring rate: 85 rpm;

[0028] Solid-liquid ratio: 1:10 (g / mL);

[0029] The reaction is terminated by rapid quenching (temperature is reduced to room temperature within 5 minutes).

[0030] Further preferably, the temperature of the hydrothermal liquefaction treatment in step (3) is 240℃, 270℃, or 300℃, and the reaction time is 60 minutes.

[0031] Further, the product separation and purification conditions in step (4) are as follows:

[0032] For the PA6 system: vacuum filtration (0.45 μm filter membrane) is used for separation, and the filtrate is used for CPL recovery;

[0033] For the PC system: ethyl acetate extraction is used to separate the oil phase product;

[0034] For the co-treatment system: first, the water phase CPL is recovered, and then the oil phase phenolic extraction is performed.

[0035] The application realizes the synergistic depolymerization of PA6 and PC by using the special environment of hydrothermal reaction. Under the condition of 270℃ / 60min: the solid hydrolysis degree of PA6 reaches 100%; the oil phase yield of PC reaches 79.78%; and the yield of CPL remains 33.98% (without significant reduction). Compared with single treatment, the reaction temperature is reduced by 30-50℃, and the energy consumption is significantly reduced.

[0036] The application achieves the following technical effects:

[0037] (1) Breakthrough in synergistic efficiency:

[0038] PA6 / PC co-treatment realizes double 100% hydrolysis degree at 270℃ (compared with single treatment of PA6: 75%, PC: 34.2%), and the energy consumption is reduced by 25% compared with single treatment;

[0039] Oil yield 79.78% (compared with single treatment 21.36%).

[0040] (2) Industrialization advantage:

[0041] Adapt to mixed plastics (PA6:PC=1:1);

[0042] Solid residue rate <5%. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The figure is the degradation degree of plastics at different temperatures;

[0044] Figure 2 The figure is the recovery rate of identified compounds in PC hydrothermal oil under different reaction conditions;

[0045] Figure 3 The figure is the caprolactam yield of different reactions; DETAILED DESCRIPTION

[0046] The technical solutions of the application will be further described below in combination with the drawings. The application provides a synergistic treatment method for polyamide 6 and polycarbonate co-hydrothermal liquefaction, and the steps are as follows:

[0047] (1) Pretreat the PA6 and PC raw materials;

[0048] (2) Mix the pretreated PA6 and PC according to the proportion;

[0049] (3) Hydrothermal liquefaction treatment of the obtained mixture;

[0050] (4) Separate and purify the product after hydrothermal liquefaction treatment;

[0051] (5) The separated liquid phase product is used for monomer recovery;

[0052] (6) The separated solid residue is subjected to subsequent treatment.

[0053] In some embodiments of the present application, the raw material pretreatment in step (1) comprises the following steps:

[0054] (1) PA6: raw material with density 1.084 g / cm 3 , melting point 220℃, particle size 30 mesh is selected;

[0055] (2) PC: raw material with melt index 5 g / 10 min (300℃ / 1.2 kg) is selected;

[0056] (3) The water content needs to be removed by vacuum drying at 60℃ for 12 hours before use.

[0057] In some embodiments of the present application, the mass ratio of PA6 to PC in step (2) is 1:1, which ensures the full interaction of the two plastic degradation products and realizes synergistic depolymerization.

[0058] In some embodiments of the present application, the specific conditions of the hydrothermal liquefaction treatment in step (3) are as follows:

[0059] Reaction pressure: autogenous pressure (about 10 MPa);

[0060] Stirring rate: 85 rpm;

[0061] Solid-liquid ratio: 1:10 (g / mL);

[0062] The reaction is terminated by rapid quenching (temperature is reduced to room temperature within 5 minutes).

[0063] In some embodiments of the present application, in step (3), the temperature of the hydrothermal liquefaction treatment is 240-300℃, and the reaction time is 60 minutes.

[0064] In some embodiments of the present application, the product separation and purification conditions in step (4) are as follows:

[0065] For PA6 system: vacuum filtration (0.45 μm filter membrane) is used for separation, and the filtrate is used for CPL recovery;

[0066] For PC system: ethyl acetate extraction is used to separate the oil phase product;

[0067] For co-treatment system: first perform water phase CPL recovery, and then perform oil phase phenolic extraction.

[0068] Compared with the traditional single-component treatment, the present application has the following advantages:

[0069] The main advantages of the present application compared with the prior art are:

[0070] 1. Compared to traditional single-plastic hydrothermal treatment technologies, this method significantly improves plastic depolymerization efficiency through the synergistic co-treatment of PA6 and PC. At 270°C / 60 minutes, the PA6 solid hydrolysis degree increased from 75.0% to 100% for single-plastic hydrothermal treatment, and the PC oil phase yield increased from 21.36% to 79.78%, achieving efficient depolymerization of mixed plastics.

[0071] 2. The present invention fully utilizes the synergistic effect of the two plastic degradation products, while maintaining the CPL yield (38.8%→33.98%) basically unchanged, while reducing the reaction temperature by 30-50°C, significantly reducing energy consumption and processing costs.

[0072] 3. This method avoids the use of strong acid / base catalysts in traditional processes and achieves efficient depolymerization through the catalytic action of the plastic's own degradation products, which not only reduces secondary pollution but also simplifies the subsequent product separation and purification steps.

[0073] 4. This invention provides a new approach to the resource recovery of mixed engineering plastic waste. By optimizing the co-processing process parameters, the synergistic conversion of PA6 and PC is achieved, providing an efficient and environmentally friendly solution for the treatment of mixed plastic waste commonly found in actual production.

[0074] Example 1:

[0075] (1) Take 0.5 g of PC, place it in a hydrothermal reactor, and add 5 mL of deionized water.

[0076] (2) Hydrothermal liquefaction was performed at 240°C for 1 h.

[0077] (3) Separating the solid-liquid hydrothermal liquefaction product of (2).

[0078] (4) The oil yield is 1.00%.

[0079] (5) Solid hydrolysis degree: 2.7%.

[0080] Example 2:

[0081] (1) Take 0.5 g of PA6, place it in a hydrothermal reactor, and add 5 mL of deionized water.

[0082] (2) Hydrothermal liquefaction was performed at 240°C for 1 h.

[0083] (3) Separating the solid-liquid hydrothermal liquefaction product of (2).

[0084] (4) The yield of caprolactam was 2.43%.

[0085] (5) Solid hydrolysis degree: 29.6%.

[0086] Example 3:

[0087] (1) Take 0.25 g of PA6 and 0.25 g of PC, mix uniformly, place in a hydrothermal reactor, and add 5 mL of deionized water.

[0088] (2) Hydrothermal liquefaction is carried out at 240°C for 1 h.

[0089] (3) The hydrothermal liquefaction product of (2) is separated into water and oil.

[0090] (4) The oil yield is 0.49%.

[0091] (5) The caprolactam yield is 4.60%.

[0092] (6) The solid hydrolysis degree is 30.7%.

[0093] Example 4:

[0094] (1) Take 0.5 g of PC, place in a hydrothermal reactor, and add 5 mL of deionized water.

[0095] (2) Hydrothermal liquefaction is carried out at 270°C for 1 h.

[0096] (3) The hydrothermal liquefaction product of (2) is separated into solid and liquid.

[0097] (4) The oil yield is 21.36%.

[0098] (5) The solid hydrolysis degree is 34.2%.

[0099] Example 5:

[0100] (1) Take 0.5 g of PA6, place in a hydrothermal reactor, and add 5 mL of deionized water.

[0101] (2) Hydrothermal liquefaction is carried out at 270°C for 1 h.

[0102] (3) The hydrothermal liquefaction product of (2) is separated into solid and liquid.

[0103] (4) The caprolactam yield is 38.80%.

[0104] (5) The solid hydrolysis degree is 75.0%.

[0105] Example 6:

[0106] (1) Take 0.25 g of PA6 and 0.25 g of PC, mix uniformly, place in a hydrothermal reactor, and add 5 mL of deionized water.

[0107] (2) Hydrothermal liquefaction is carried out at 270°C for 1 h.

[0108] (3) The hydrothermal liquefaction product of (2) is separated into water and oil.

[0109] (4) Oil yield was 79.78%.

[0110] (5) Caprolactam yield was 33.98%.

[0111] (6) Solid hydrolysis degree was 100.0%.

[0112] Example 7:

[0113] (1) Take 0.5 g of PC, place it in a hydrothermal reactor, and add 5 mL of deionized water.

[0114] (2) Perform hydrothermal liquefaction at 300°C for 1 h.

[0115] (3) Solid-liquid separation of the hydrothermal liquefaction product of (2).

[0116] (4) Oil yield was 72.51%.

[0117] (5) Solid hydrolysis degree was 100.0%.

[0118] Example 8:

[0119] (1) Take 0.5 g of PA6, place it in a hydrothermal reactor, and add 5 mL of deionized water.

[0120] (2) Perform hydrothermal liquefaction at 300°C for 1 h.

[0121] (3) Solid-liquid separation of the hydrothermal liquefaction product of (2).

[0122] (4) Caprolactam yield was 81.07%.

[0123] (5) Solid hydrolysis degree was 100.0%.

[0124] Example 9:

[0125] (1) Take 0.25 g of PA6 and 0.25 g of PC, mix them evenly, place them in a hydrothermal reactor, and add 5 mL of deionized water.

[0126] (2) Perform hydrothermal liquefaction at 300°C for 1 h.

[0127] (3) Water-oil separation of the hydrothermal liquefaction product of (2).

[0128] (4) Oil yield was 50.42%.

[0129] (5) Caprolactam yield was 78.99%.

[0130] (6) Solid hydrolysis degree was 100.0%.

[0131] The above technical solutions of the present application are illustrated by examples. The attached figures show the degradation degree of plastics at different temperatures, and the attached Figure 1 It can be seen that when the reaction condition is 270℃ for 60min, the hydrolysis degree of the PA6 and PC co-processing solid can reach 100%, and at this time, the hydrolysis degree of PC and PA6 alone is 34.2% and 75.0% respectively at 270℃. When the temperature reaches 300℃, the hydrolysis degree of PC and PA6 alone can reach 100%, which shows that the co-processing of PC and PA6 can reduce the reaction conditions. Figure 2 The attached figures show the recovery rate of identified compounds in PC hydrothermal oil under different reaction conditions, and the attached Figure 2 It can be seen that, Figure 2 It can be seen that, when the reaction condition is 270℃ for 60min, the hydrolysis degree of the PA6 and PC co-processing solid can reach 100%, and at this time, the hydrolysis degree of PC and PA6 alone is 34.2% and 75.0% respectively at 270℃. When the temperature reaches 300℃, the hydrolysis degree of PC and PA6 alone can reach 100%, which shows that the co-processing of PC and PA6 can reduce the reaction conditions. Figure 3 The attached figures show the recovery rate of identified compounds in PC hydrothermal oil under different reaction conditions, and the attached Figure 3 It can be seen that, Figure 3 It can be seen that, when the reaction condition is 270℃ for 60min, the hydrolysis degree of the PA6 and PC co-processing solid can reach 100%, and at this time, the hydrolysis degree of PC and PA6 alone is 34.2% and 75.0% respectively at 270℃. When the temperature reaches 300℃, the hydrolysis degree of PC and PA6 alone can reach 100%, which shows that the co-processing of PC and PA6 can reduce the reaction conditions.

[0132] It needs to be further explained that the above embodiments are only used to understand the technical solutions of the present application, and are not used to limit the protection scope of the present application. Any obvious adjustment and modification of the technical solutions of the present application which belongs to the technical concept of the present application should also belong to the protection scope of the present application.

Claims

1. A synergistic process for the hydrothermal liquefaction of polyamide 6 and polycarbonate, characterized by the steps of As follows: (1) Pretreatment of PA6 and PC raw materials; (2) Mixing of pretreated PA6 and PC according to a proportion; (3) Hydrothermal liquefaction treatment of the obtained mixture; (4) Separation and purification of the product after hydrothermal liquefaction treatment; (5) Use of the separated liquid phase product for monomer recovery; (6) Subsequent treatment of the separated solid phase residue; In step (2), the mass ratio of PA6 to PC is 1:1; in step (3), the temperature of hydrothermal liquefaction treatment is 240-300℃, and the reaction time is 60 minutes.

2. The synergistic process for the hydrothermal liquefaction of polyamide 6 and polycarbonate according to claim 1, characterized in that, The raw material pretreatment in step (1) includes the following steps: (1) PA6: raw material with a density of 1.084 g / cm 3 , a melting point of 220°C, and a particle size of 30 mesh; (2) PC: raw material with a melt index of 5g / 10min (300℃ / 1.2kg) is selected; (3) The raw material needs to be dried at 60℃ under vacuum for 12 hours before use to remove water.

3. The synergistic process for the hydrothermal liquefaction of polyamide 6 with polycarbonate according to claim 1, characterized in that, The mass ratio of PA6 to PC in the mixture is 1:

1.

4. The synergistic process for the hydrothermal liquefaction of polyamide 6 with polycarbonate according to claim 1, characterized in that, The specific conditions of the hydrothermal liquefaction treatment in step (3) are as follows: Reaction pressure: autogenous pressure 10MPa; Stirring rate: 85rpm; Solid-liquid ratio: 1:10g / mL; Reaction termination by rapid quenching, cooling to room temperature within 5 minutes.

5. The synergistic process for the hydrothermal liquefaction of polyamide 6 with polycarbonate according to claim 1, characterized in that, The temperature of hydrothermal liquefaction treatment in step (3) is 270℃, and the reaction time is 60 minutes.

6. The synergistic process for the hydrothermal liquefaction of polyamide 6 with polycarbonate according to claim 1, characterized in that, The product separation and purification conditions in step (4) are as follows: For PA6 system: 0.45μm filter membrane vacuum filtration separation, filtrate for CPL recovery; For PC system: ethyl acetate extraction to separate oil phase product. For co-treatment system: first water phase CPL recovery, then oil phase phenolic extraction.

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